Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$100.33	7.711%	$108.0664	$108.07	$108.05	$108.10
Purchase #2	$230.79	12.817%	$260.3704	$260.37	$260.35	$260.40
Purchase #3	$212.92	3.192%	$219.7164	$219.72	$219.70	$219.70
Purchase #4	$140.71	9.492%	$154.0662	$154.07	$154.05	$154.10
Purchase #5	$48.48	13.323%	$54.939	$54.94	$54.95	$54.90
Purchase #6	$208.75	5.635%	$220.5131	$220.51	$220.50	$220.50
Purchase #7	$99.56	10.311%	$109.8256	$109.83	$109.85	$109.80
7 purchase totals =	$1,041.54		$1,127.4971	$1,127.51	$1,127.45	$1,127.50